Process for purification of phosphate esters

ABSTRACT

A crude phosphate ester product can be purified by first washing it with chelating agent composition (such as a dilute acidic solution) and then, preferably, water, drying the resulting product, and then treating the resulting product with an acid scavenger, as exemplified by an epoxy-containing compound, such as 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexyl carboxylate.

This application is a 371 of PCT/US02/03522, filed Feb. 8, 2002, andclaims benefit of 60/267,259, filed Feb. 8, 2001.

The present invention is useful in the purification of phosphate estercompositions, in general, with aromatic oligomeric phosphate estercompositions being a preferred class of material for treatment.

For example, aromatic oligomeric phosphates, which are used as flameretardants for thermoplastic resins, are made by reaction of POCl₃ witha biphenol or a diol followed by reaction with phenol (or,alternatively, by reaction of diphenyl chlorophosphate with a biphenol)in the presence of a Lewis acid catalyst to form what is termed a “crudephosphate” composition. Usually, extensive washing of this type ofproduct is needed to remove catalyst residues (for example, such metalspecies as magnesium, aluminum, zinc, and titanium) and other acidicimpurities that may negatively impact the properties of polymers (forexample, polycarbonates, polyesters, and the like) to which the flameretardant is to be added.

In Examples 1 to 6 of U.S. Pat. No. 5,616,768 to S. Kawata, such areaction product is washed with an acidic aqueous solution to remove thecatalyst and is then dried under reduced pressure. In Examples 1 to 14of the same patent, the crude ester is treated with an epoxy compound atelevated temperature, washed with water, heated for a certain time andwashed again with water. The oil layer is then dried under reducedpressure to give a purified product. This process is cumbersome andinvolves two wash and two drying sequences.

The present invention is a new, simplified purification process toobtain a product of low metal content and low acidity. This new processcomprises washing the reaction product with a dilute solution of achelating agent. As used herein, the term “chelating agent” is intendedto encompass those molecules and ions that can bond to a metal cation.Examples suitable chelating agent compositions for use herein includedilute acidic aqueous solutions that comprise an Arhenius acid, such ashydrochloric acid, phosphoric acid, carboxylic acids, a phosphonic acid,sulfuric acids, sulfonic acids, and the like. Also solutions containingsuch chelating agent as ethylenediamine or ethylenediaminetetraaceticacid (EDTA) can also be employed. The process herein involves washingthe crude reaction product with such a chelating agent, followed,preferably, by one or two water washes to remove the catalyst. Thechelating agent is essential to effect the removal of Lewis acidcatalyst residues (see Comparative Example 1). The chelating agenttreatment preferably takes place at temperatures that range from about40° C. to about 90° C. using an amount of chelating agent, on an activebasis, that ranges from about equimolar to about 100% over equimolar.The use of temperatures near the upper limit of the aforementionedtemperature range will result in a shorter time within which the desiredreaction of chelating agent and metal occurs.

The use of the preferred water washes following the dilute chelatingagent wash allow for removal of excess chelating agent from thephosphate ester oil, thereby contributing to a decrease in acidity (see,for example, Example 2, which follows).

The crude product is then preferably dried under reduced pressure,filtered and is then treated with an acid scavenger. Drying of the crudeproduct prior to treatment with the acid scavenger is also important tothe process of this invention since the presence of water impedes theaction of the acid scavenger additive (see, for example, Example 9,which follows).

Useful, representative acid scavengers are compounds containing epoxygroups. Examples of suitable epoxy compounds that can be used inaccordance with the present invention include ethylene oxide, propyleneoxide, cyclohexene oxide, styrene oxide, epoxidized soybean oil,3,4-epoxycyclohexyl-methyl-3,4-epoxy-cyclohexane-carboxylate, vinylcyclohexene dioxide,2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane,bis(3,4-epoxycyclohexyl)adipate, 1,2-epoxy-p-vinylcyclohexene, BisphenolA epoxy resins (for example, ARALDITE®, a brand name of Ciba SpecialtyChemicals), and the like. In general, it is preferred that the number ofequivalents of epoxy used be equal to or greater than the number ofequivalents of acid present in the crude phosphate ester based on theTotal Acid Number (“TAN”) of the crude phosphate ester. Total AcidNumber is defined as the number of milligrams of potassium hydroxiderequired to neutralize one gram of sample, the determination of which isdescribed in ASTM method D974. The treatment with the acid scavenger cantake place at temperatures that can range from about 25° C. to about200° C. The amount of acid scavenger that is employed, on an activesbasis, can generally range from about stoichiometric amount to about100% excess, based on the acid number.

The Examples that follow illustrate this invention.

EXAMPLE 1 Synthesis of Reaction Mixture

To 1249.2 g. of “DPCP mix” (this mixture contains mainly diphenylchlorophosphate, “DPCP”, and small amounts of monophenyldichlorophosphate and triphenyl phosphate) and 4.2 g. of magnesiumchloride, which was heated to 140° C. under 50 mm vacuum, wascontinuously added 513 g. of bisphenol A over an eight hour period. Atthe end of this addition, the reaction mixture was held at 140° C. foran additional three and one half-hours. The resulting crude phosphateester had an acid number of 4.4 mg. KOH/g. The magnesium content of thecrude product was 2600 ppm.

EXAMPLE 2 Purification of Reaction Mixture

Step 1: To 1200 g. of 0.4% oxalic acid in water, which was heated to 90°C. with stirring, was added 1000 g. of the reaction mixture fromExample 1. The mixture was agitated for thirty minutes and was allowedto separate. The acid number of the oil was 0.74 mg. KOH/g. The oillayer was washed twice with water at 65° C. and was dried under vacuumto give 913.2 g. of product. The magnesium content of this product was20 ppm, and the acid number was 0.48 mg. KOH/g.

Step 2: To the oil from step 1 of this Example (acid number=0.48 mg.KOH/g) was added, with stirring at 65° C., 1.39 g. of 3,4-epoxycyclohexyl methyl-3,4-epoxy cyclohexyl carboxylate, “ERL 4221” brand (abis epoxide product available from Union Carbide). After four hours, theacid number of the resulting Bisphenol A bis(diphenyl phosphate)product, “BDP”, was 0.019 mg. KOH/g.

Examples 3 to 5, which follow, show alternative embodiments forpracticing just step 1 of the purification of the reaction mixture thatwas previously exemplified.

EXAMPLE 3 Purification of Reaction Mixture

Step 1: To 600.3 g. of 1% phosphoric acid in water, which was heated to90° C. with stirring, was added 503.8 g. of the reaction mixture fromExample 1. The mixture was agitated for ninety minutes and was allowedto separate. The acid number of the oil was 0.45 mg. KOH/g. The oillayer was washed once with water at 65° C. and was dried under vacuum togive 512.0 g. of product. The magnesium content of this product was 38ppm, and the acid number was 0.28 mg. KOH/g.

EXAMPLE 4 Purification of Reaction Mixture

Step 1: To 550 g. of 0.8% DEQUEST sequestrant 2010(1-hydroxyethylidene-1-1-diphosphonic acid, from Solutia) in water,which was heated to 90° C. with stirring, was added 445.8 g. of thereaction mixture from Example 1. The mixture was agitated for ninetyminutes and was allowed to separate. The acid number of the oil was 1.22mg. KOH/g. The oil layer was washed once with water at 65° C. and wasdried under vacuum to give 444.1 g. of product. The magnesium content ofthis product was 40 ppm, and the acid number was 0.29 mg. KOH/g.

EXAMPLE 5 Purification of Reaction Mixture

Step 1: To 605.5 g. of 0.9% BAYHIBIT AM (2-Phosphono-1,2,4-butanetricarboxylic acid, from Bayer) in water, which was heated to 90° C.with stirring, was added 504.7 g. of the reaction mixture fromExample 1. The mixture was agitated for ninety minutes and was allowedto separate. The acid number of the oil was 0.28 mg. KOH/g. The oillayer was washed once with water at 65° C. and was dried under vacuum togive 504.7 g. of product. The magnesium content of this product was 11ppm, and the acid number was 0.21 mg. KOH/g.

Examples 6-8, which follow, show alternative embodiments for practicingjust step 2 of the purification of the reaction mixture.

EXAMPLE 6 Purification of Reaction Mixture

Step 2: To 1216 g. of crude BDP that was previously washed with oxalicacid and water as described in step 1 of Example 1 (acid number=0.48 mg.KOH/g and magnesium content=11 ppm) was added, with stirring at 110° C.,1.65 g. of 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexyl carboxylate,“ERL 4221” brand (a bisepoxide product available from Union Carbide).After ninety minutes, the acid number of the resulting Bisphenol Abis(diphenyl phosphate) product, “BDP”, was 0.017 mg. KOH/g.

EXAMPLE 7 Purification of Reaction Mixture

Step 2: To 1232 g. of crude BDP that was previously washed with oxalicacid and water as described in step 1 of Example 1 (acid number=0.48 mg.KOH/g and magnesium content=11 ppm) was added, with stirring at 130° C.,1.68 g. of 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexyl carboxylate,“ERL 4221” brand (already described earlier. After 45 minutes, the acidnumber of the resulting Bisphenol A bis(diphenyl phosphate) product,“BDP”, was 0.019 mg. KOH/g.

EXAMPLE 8 Purification of Reaction Mixture

Step 2: To 600 g. of crude BDP that was previously washed with oxalicacid and water as described in step 1 of Example 1 (acid number=0.53 mg.KOH/g and magnesium content=13 ppm) was added, with stirring at 65° C.,0.63 g. of propylene oxide. After six hours, the acid number of theresulting Bisphenol A bis(diphenyl phosphate) product, “BDP”, was 0.054mg. KOH/g.

EXAMPLE 9 Purification of Reaction Mixture

Step 2: To 1000 g. of crude resorcinol bis(diphenyl phosphate), “RDP”,that was previously washed with oxalic acid and water as described instep 1 of Example 1 (acid number=0.30 mg. KOH/g and magnesium content=6ppm) was added, with stirring at 70° C., 5.0 g. of 3,4-epoxy cyclohexylmethyl-3,4-epoxy cyclohexyl carboxylate, “ERL 4221” brand. After threehours, the acid number of the resulting Resorcinol bis(diphenylphosphate) product, “RDP”, was 0.014 mg. KOH/g.

EXAMPLE 10 Effect of Water on Acid Reduction

In this Example, 250 g. of wet bisphenol A bis(diphenyl phosphate),“BDP”, (no drying step after washing with oxalic acid and water;containing 4-5% water), having an acid number 0.19 mg. KOH/g., wastreated with 0.1214 g. of “ERL 4221” bis epoxide at 65° C. for fourhours, producing a product having an acid number of 0.15 mg. KOH/g.

COMPARATIVE EXAMPLE 1 Effect of Magnesium on Acid Reduction

Step 1: To 705.0 g. of water, which was heated to 90° C. with stirring,was added 614.7 g. of the reaction mixture from Example 1. The mixturewas agitated for sixty minutes and was allowed to separate. The acidnumber of the oil was 1.1 mg. KOH/g. The oil layer was washed once morewith water at 65° C. and was dried under vacuum to give 599.1 g. ofproduct. After filtration of the oil, the magnesium content of thisproduct was 160 ppm, and the acid number was 0.58 mg. KOH/g.

Step 2: To 507.4 g. of the oil from step 1 (acid number=0.58 mg. KOH/g)was added, with stirring at 110° C., 1.71 g. of 3,4-epoxy cyclohexylmethyl-3,4-epoxy cyclohexyl carboxylate, “ERL 4221” brand. After onehour, the acid number of the resulting bisphenol A bis(diphenylphosphate) product, “BDP”, was 0.238 mg. KOH/g. Addition of supplementalERL 4221 bis epoxide at 110° C. for one hour did not decrease the acidnumber.

The described mode of operation is batch, but the method is notrestricted to batch operation. It can as well be performed in acontinuous mode.

The foregoing Examples should not be construed in a limiting fashionsince they merely relate to certain preferred embodiments of the presentinvention. The scope of protection desired is set forth in the claimsthat follow.

1. A process for purifying crude bisphenol A bis(diphenyl phosphate),said process consisting essentially of washing said crude bisphenol Abis(diphenyl phosphate) with an aqueous acidic chelating agentcomposition and then, optionally, with water, to provide a washedbisphenol A bis(diphenyl phosphate), drying the resulting washedbisphenol A bis(diphenyl phosphate), to provide a dried bisphenol Abis(diphenyl phosphate) and treating the dried bisphenol A bis(diphenylphosphate) with an epoxy group containing acid scavenger.
 2. A processaccording to claim 1 in which the epoxy group containing acid scavengeris 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexyl carboxylate.
 3. Aprocess according to claim 1 in which washing with the chelating agentcomposition takes place at a temperature of from about 40° C. to about90° C.
 4. A process according to claim 1 in which treatment with acidscavenger takes place at a temperature of from about 25° C. to about200° C.
 5. A process according to claim 1 in which the number ofequivalents of epoxy group containing acid scavenger is equal to orgreater than the number of equivalents of acid present in the crudebisphenol A bis(diphenyl phosphate) based on the acid number of thecrude bisphenol A bis(diphenyl phosphate).
 6. A process according toclaim 1 in which the dried bisphenol A bis(diphenyl phosphate) istreated with the epoxy group containing compound at a temperatureranging from about 40° C. to about 200° C.